Electric cable and cable joint



Feb. 14, 1950 1 WETHERILL 2,497,706

ELECTRIC CABLE AND CABLE JOINT Filed Feb. 2l, 1945 2 SheeS-Shee l Figi )6 38 09,7 f 6 vl v /lv -Il/ l a IIIIIIIIIIIIIIIIIIIIIIIIIIII hventOP: Lgnh Wetherll,

Feb. 14, 1950 l.. WETHERILL ELECTRIC CABLE AND CABLE JOINT 2 Sheets-Sheet 2 Filed Feb. 2l, 1945 SOLID /NZ oF CABLE n MCE/WER Lm: oF CABLE n. u., PPM@ OMV/Wn tt P nerf@ w nn 11n/H lu/ n: b

watentecl Feb. 14, 195C 2,497,706 ELECTRIC CABLE AND CABLE JOINT Lynn Wethcrill, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application February 21, 1945, Serial No. 578,965

4 Claims.

My invention relates to electric cables and more particularly to electric cables provided with connectors for making joints between lengths of various types of cable. More specifically the invention relates to cables and connectors therefor which are particularly adapted for the transmission of high frequency currents of the order of several hundred megacycles.

My invention is of particular interest in connection with cables having solid dielectric medium between the inner and outer conductors in which lengths of the cable are connected to other cables by means of connectors employing different dielectric medium from that used in the cable. Sometimes joints using a solid dielectric medium may be used but usually the medium is gaseous, such as air. One advantage of using air as the dielectric medium at the cable joint is that it permits quick assembling and dismantling of such cable connections in field use. At the same time, the connection or joint between cable sections must be so constructed that the separable parts thereof may be quickly and easily attached to lengths of cable cut from bulk stock.

It is of particular importance in cable lengths used with high frequency currents that the characteristic impedance, or surge impedance, of the alone will not suflice to give highest efficiency in y a high frequency transmission line incorporating joints. I have found that it is also important to so construct the cable joint that no reflection of the high frequency waves occurs at faces between different dielectric media, particularly where the diameters of the inner and outer conductors have been changed as at the cable joint. Otherwise, spurious or unwanted standing waves may result with consequent loss of power in the transmission line.

It is an object of my invention to provide a newI l and improved arrangement of cable lengths having a joint therein which is so constructed as to provide substantially constant surge impedance throughout its length. and in which the refraction of a high frequency wave at the joint is so controlled as to reduce reflections to a minimum.

Such variations in diameters almosty It is another object of my invention to provide a new and improved cable joint having a conhector which may be easily and quickly attached to the severed end of a cable and which when assembled on the cable provides a boundary surface substantially precluding reections of high frequency waves and giving substantially constant surge impedance through a joint formedfrorn the connector.

It is a further object of my invention to provide a new and improved method of fastening the connector of a cable joint structure to the severed end of the cable which method may be employed equally well in the field as in the factory.

A still further object of my invention is to provide a new and improved apparatus for making a cable joint of the type described.

In the accompanying drawing, Fig. 1 illustrates lmatic views illustrating the principles by which electric energy is transmitted through a high frequency cable and joint constructed according tomy invention.

It is well known that the characteristic impedance, or surge impedance, Z of an electricv cable or of any small part thereof may be ex- L=inductance in henries per unit length C=capacitance in farads per unit length.

This term may also be expressed as R Z 10g, r

in which k=dielectric constant of the insulating medium between the inner and outer conductors. v R=inner diameter of the outer conductor and r=outer diameter of the inner conductor.

From this formula, it will be seen that thel characteristic impedance of the cable is a funcy cable.

tion of three variables 1c, R, and r. If any one of these variables is changed, a corresponding change will be necessary in the remaining variables if the characteristic impedance of the cable is to be maintained constant throughout its length. l

In cases where it is desired to utilize cable joints having `separable connectors for taking lengths of cable apart, provision must be made for connecting together the inner and outer conductors of the cable length. This means that some form of connector must be--fastenedto the inner conductor. Almost invariably the connector is of a diameter greater lthan Ithatof the inner conductor of the high frequency cable. Furthermore, it is highly desirable to employ a gas insulating medium, such-as air,-at the Acable joint so that no diiiculty will be experienced in taking the joint apart infield use.l It will thus beseen ,that if theequation is "to be followed throughout the entire length ofthe cableincluding,thecable joints, variations inthe sizeof theihnerand outerconductors will accur at thecable joints `and also the spacing between the conductors will vary because the dielectric lconstant for .the insulating medium between thefconductors v,has been changed.

In the form ofniy linvention illustrated, I have shown a `coaxial high frequency `cable in which a -solid Ydielectric medium is employed, such as polyethylene. Thismaterialhas adielectric constant of about 2.4. Furthermore, `I h-avechcsen to illustrategsuchtacableas being provided with connectors forming-a cable joint inlwhich air is utilized as a v,gaseous dielectric medium between the innerand cuter'conductors. The dielectric constant of airisL Sincethe dielectric constant of air is less than.that-.of polyethylene, the `ratio Rl/r in the jointmust be smaller than for the cable. Sincedielectric strength of air is less than that of polyethylene, the spacing between the conductors at the jointinustbe increasedin order not to lower theoverall dieleGtricstrength of the vZF outer conductorsfoftheAv cable have ,been so chosen in Arela-tion tothe dielectric medium as to make the characteristic'.impedance of the joint substantially equal to that of the cable. ,In order to match the characteristictor-,surge impedance of the joint vto that of the cable, and in order to connect thelarge damB-erconductors of the joint to the relatively smaller conductors of thecable, a portion of the joint is formed with tapered conductors so that the diameters and spacing of the conductors of the cable are gradually increased to those of the joint. This arrangement is shown by Fig. 1.

Although the characteristic limpedance of the joint has been Vmatched to that of the cable, this requirement algneisnctsuilcient to attain maximum efficiency in the transmission line. It is also important to so constructthe cable joint that no reflections of high frequency waves occur as the wave passes down the cable. Heretofore, the dielectric medium in the cable has been terminated abruptly whenever the cable has been connected 'to a joint -havinga different dielectric medium. vThis has almost 4invariably resulted in reflection of part of lthe wave in those instances in which there Lis a change `in the diameters of the innerand outer conductorsat cable joints. However, I have found that the interface However, the.. diame ters of vthe inner and between the two dielectric mediums of the cable and joint may be so positioned as to substantially preclude reflections of the high frequency wave :and at the same time give a substantially constant surge impedance at the joint. The wave is retracted so that it passes from one dielectric medium to the other with substantially no reflection. The arrangement is particularly useful in those instances in which the diameter of the cable joint varies from that of the cable and in which tapered conductors are used in the joint to obtain auniform characteristic impedance of the transmission line. e

In Fig. '1 of the dra-wing, I have shown a cable r' and joint therefor invwhich a portion of the solid dielectric of the cable has been extended up into thecable vjoint.and.. terminated at an interface or boundary disposed at an angle. This angle is critical. It depends uponthe dielectric constants of the insulating materials used in the cable andjoint. It is so vlocated asfto keepthefoharac ter-istie impedance -of the cable substantially constant-through'the joint as well as yprecluding reflections of theYhighI-frequency'fwave. Inorder to more lfully explain themanner in which vthe anglev of the vboundary is determined, I have shown the arrangementv of the/dielectric media and boundary in the diagrammatic'views Aof Figures 8 land9. Y y

In Figure 9,'the highffrequency -wave is represented as parallel .lines moving'lalong the paths of the dielectric-media. It .remains .as nearly as.

possible perpendicular :to the boundaries formed by the conducting surfaces. The wave visshown moving .along the soliddielectric until` it reaches the boundary where it is Vretracted as it .passes into the gaseous dielectric medium. As mentioned above, theboundary :angle is critical in order Ato secure proper vrefraction .of the wave. In order to.illustrate.the=boundary.angle, va small portion of the wave front,andboundary'angle, Ias indicated byfthedottedlines in Fig. 9, have been shown in the enlarged schematic View of Fig. 8.-

Fig. 8 illustrates .thezboundary plane vseparat- Y ing the two dielectric'media .whichare indicated by theparallel dottedlines. The dotted .lines also represent the path of .the .high 7frequency wave. In'Figure 8,

B'zangle of incidence vof `the wave A=angle of refraction of the wave.

It -is assumed that ByV the sine law of refraction Since the velocity of an electric rwave is inversely proportional to the square vroot of the l. dielectric lconstant' where K1=dielectric constant of insulating material on entering side of boundary (side of incidence). I

-where K2=dielectric constant of insulating mal lterial on other side of boundary (side of re- 'fracton).

Substituting L M for V in the sine law equation, it is found that sin A JZ- sin B E sin A .KZSD B Thus, it is seen that to secure proper refraction of the wave the angles A and B are determined by the square root of the ratio of the dielectric constants for the insulating materials used on each side of the boundary.

In meeting the requirement for constant surge impedance on each side of the boundary, reference is made to the formula for surge impedance already mentioned in which Z an From this equation, it will be apparent that the surge impedance Z is inversely proportional to However, the equation just mentioned is that for the surge impedance of a cylindrical cable. On the other hand, the diagrammatic view of Fig. 8 shows a small rectangular strip of a dielectric medium with conductors on opposite faces. In the equations to follow, the surge impedance for such a, small rectangular strip will be derived from the equation for the surge impedance of a cylindrical cable.

Referring to Fig. 10, it will be apparent from the formula given for the surge impedance of a cable that r=the radius of the inner conductor r+t=the radius of the outer conductor As angle A in Fig. 10 grows smaller and smaller, the volume of dielectric material contained in the angle will approach a rectangular prism. The angle A includes a length a on the circumference of circle having radius r so that the surge impedance of the volume in angle A is By comparing Figs. 1G and 8, it will be apparent that the distance t in Fig. 10 corresponds to GF in Fig. 8. Assuming that Z1=surge impedance on the entering side of the boundary Z2=surge impedance on the opposite side of the boundary,

then

f er n1/r. par vn vis to incorporate both factors in determining the u1- timate values of angles A and B. Thus E cos B sin A Kgncos A sin B Let r= lil T cos B r sin A cos A *sin B sin2 A Ir2 cosL A=cos2 B sm2 B= sin2 A r2 cos2 A+ T2 =cos2 B-l-sm2 B=l l COSA-JW By trigonometry cos A (Equation l) Substituting Equation 1 But by the previous equation E cos B Kzcos A adscritos* Comparing the two equations sin A=cos Bi This solution gives` values for angles A and B such that l K1 tan. A K2 K1 cot B TQ Thus it will be seen that the boundary angle is determined by the ratio of the dielectric constants of the insulating materials on each side of the boundary. For the special' case in which air, having a dielectric constant of 1, is used on one side of the boundary the expression N/ becomes since K2=1 In the showing of Figs. 1, 8 and 9, and in the mathematical steps; set forth above, the electric wave has been considered as passing from a solid dieectric medium into a gaseous one. This has been done in the interest of simplification and to make the functions of the boundary more clearly apparent. However, it should be realized that the electric wave also travels in a reverse direction, i. e., from the gaseous to the solid dielectric medium. In such instances, the angles A and B in the equations mentioned above would be reversed. Similarly, Z1 and Zz would` be reversed as would K1 and m.

Turning now to the actual construction of my invention shown by Fig. 1, two cable sections I and 2 are joined together with a connector 3. Each cable section has an inner conductor 4 and an outer conductor 5, in the presentinstance made of breidt-:d material and concentrically spaced from the inner conductor 4. The annular tan A= cot B= space between the conductors is ,filled` with insuf.;

lating material, in the present example, a solid dielectric 6, such as polyethylene. The outer conductor 5 is protected by a jacket T made from suitable material such as polyvinyl chloride.

The connector 3 for connecting two` cable sectol'is i includes means for securing and electrically connecting such terminals together. Each terminal comprises a casing 8 which has a ,substantially cylindrical end portion 9, a substantially conical' or tapered intermediateportion I and a substantially cylindrical end portion II". The cylindrical casing portion 9 forms a packing chamber to receive the severed end of the cable. A braid3 clamp l2 is located in said chamber between an outwardly turned portion of the braided outer conductor and the jacket 1. The jacket l is securely sealed to the casing 9 and the outer conductor is securely connected to the casing 9 by means of suitable packing rings I3 and washers l@ held in position` by a gland nut I5 threaded into the casing 9. In this way, the outer conductor 5 is electrically connected tothe joint casing 8.

The inner conductor 4 within the end casing Il carries a metallic cone I6 which has its apex near the casing portion 9^ and its base within the. cylindrical casing portion Il., The surface of the cone is roughly parallel to: the inner surface of conical intermediate portion I6. Together these and 2 is made up of two terminals andelements form taperedsurfaces for maintaining approximately uniform surge impedancethrough the joint as the small diameter conductors of the cable merge with the larger ones off the joint. The metallic cone I6 hasl an extension I'l with a threaded collar I8. The cone is secured to and electrically connected with the conductor 4 by any suitable means such as solder I9 filling an opening in the cylindrical portion I1. A sleeve 20 is threaded at one end to the threaded collar I8 of the cone I6. Each of the two terminals on the two lengths of cable to be connected together' has the elements 6 to 2U described above. The sleeves 2B of the twol terminals are electrically connected by means of a connecting member 2| which has an end portion 22 disposed within one of the sleeves 2li and' preferably brazedor fused thereto. The connecting member' 2I has an in-` termediate portion or collar located between and forming abutments for the adjacent ends of the sleeves 2t of the terminals. The connecting v memberi'n addition has a slotted cylindrical por'- tion 23 forming a snug fit in the other of the" sleeves 20 so that a good electrical connection isv obtained between the sleeves.

The casings 8 of the terminals are electrically andmechancally securely connected together by a suitable coupling. In the present example, the

casing 8 of the left-hand terminal is provided with a lianged extension 24 secured to the casing by suitable means such as solder 25. The casing 8 of the right-hand terminal is. provided with'.

another flanged extension 26 suitably secured to thev casing. The iiangedV extensions are sealed--v together byV means including a packing ring 21?' and allanged nut 28.

The soliddielectric E has a conical end face or boundary 2S and is held in position i-n tightsealing engagement with the outer conductor or casing by means of a sealing gasket 30 engagingvv 33 formed between the inner and outer conductors. of the connector 3 is filled with a gaseous dielec- ,I

However, it. will be apparent' tric such as air. that other gases may be used', such as nitrogen. Also in certain instances, the space 33 might be filled with insulating compound having high dielectric strengthg for example, polystyrene.

As aforementioned, the boundary surface 29 makes an angle with the dielectric media of the cable and joint such that /n tan A- K2 and cot B-\/K2 As shown by Figure 1, the angles A and B are measured from a line normal or perpendicular toY the boundary line 29 of the solid dielectricmaterial. The solid dielectric as far as it engages directly the cylindrical conductor 4 has a constant inner diameter. Adjacent the metallic cone I6 the diameter of the solid dielectricv increases gradually and reaches a maximum at or near the base of the metallic cone i6. In other words, the inner surface of the solid dielectric is substan- 15 tially conical within thecabl'e connector or termi- 9 nal and has a tangent approach to the cylindrical inner surface of the solid dielectric in the cable section. The outer surface of the solid dielectric in the connector is likewise substantially conical with slightly curved contour and a diameter increasing toward the end of the cable. The inner and outer curvatures ci the solid dielectric should be as small as possible. Practical considerations limit the length of the conical surfaces. The outer diameter of the inner cylindrical conductor and the inner diameter of the outer cylindrical conductor of the connector are chosen to produce with the chosen dielectric a uniform surge impedance equal to that of the solid cable secion.

If an electric wave is considered approaching the boundary from the solid side, it is desirable, from a theoretical standpoint, that the wave approach the boundary at the angle of incidence B, as indicated in the diagrammatic showing of Fig. 8. If this were to happen, it would mean that the contours of the inner and outer cones of the concentric conductors should approach the boundary at the same angle in order to cause the electric wave to approach at the desired angle. However, from a practical standpoint, it is not possible to have both the inner and outer cones approach the boundary at the same angle because considerations of substantially constant surge impedance require that the two curves of the cones diverge. Although it is necessary to make the cones diverge, it is possible to reduce the undesirable eiect of the divergence by making the two cones diverge from the desired angle of incidence by equal amounts and in opposite directions so that the average of the directions of the two cones will be substantially correct. This would mean that the average angle of incidence of an electric Wave would be correct. In addi- -tion to the improved cable joint thus far described, my invention contemplates a new and improved method and apparatus for constructing such a joint.

During manufacture of a cable joint or terminal according to my invention the jacket 1 is stripped back from the end portion of a cable (Fig. 2). Thereupon the gland nut I5, washers I4 and gaskets I3 are passed over the jacket 1 and the braid clamp I2 is passed over the outer conductor 5 and wedged under the jacket 1. The braid 5, forming the outer conductor of the cable, is then turned outwardly to form a flange around the braid clamp I2. The casing 8 is then passed over the cable end portion. The gland nut I5 is tightened to form a weather-proof seal between the casing 8 and the jacket -1 of the cable section.

In the present instance the inner conductor 4 and the solid dielectric 8 on the end portion extend axially beyond the casing 8. The terminal parts thus far assembled are then placed into a molding press to mold the dielectric material on the end portion into the desired shape.

The press to accomplish this, as shown in part in Fig. 2 and in full in Fig. 5, comprises a cylinder 34 forming a molding chamber. nel 35 connected to a pipe 36' and an exhaust( port 31 permits a heating medium, such as hot air, to be'circulated in the cylinder 34 during the molding operation. The cylinder 34 has a threaded end portion mounted on a supporting plate 38 and forming an inner annulus shoulder 39. The supporting plate 38 is connected to an end plate 4D'(Fig. 5) by means of four rods 4I. A plunger 42 is slidable into the-.right-hand end of thecyl- Inder 34 and-has .an end'face 4,3 which vc oniufins l A-to the predetermined shape of the boundary or An inlet chan- 6 end face 29 (Fig. 1) to be produced. The plunger has a vent channel 44 for discharging gases as the plunger passes beyond the exhaust opening 31 and for discharging some of the molded dielectric compound during the molding operation (Fig. 3), for a purpose to be described later.

As shown by Figure 5, the right-hand end of the plunger is secured to a threaded sleeve 45 and a plate 46 slidably engaging the rods 4| and acting as a guide for the plunger on said rods. The plunger is actuated, that is, moved axially by means of a screw 41 connected at its right-hand end to a handle 48 and having screw engagement with the end plate 40. The left-hand end of the screw 41 has a head 49 supported within the sleeve 45 by means of a ball-bearing 50 and is loosely connected to the plunger 42 by a slidable cup 5I and a compression spring 52. Upon clockwise rotation of the handle 48 the screw 41 is moved toward the left. This movement is transmitted through the spring 52 to the plunger 42. The spring normally acts as a shock absorber to effect uniform transmission of force from the screw to the cylinder. As the resistance to movement of the plunger increases during the molding operation the spring is compressed until the cup 5I engages directly the end face of the plunger 42, -the spring then being completely enclosed within a bore in the plunger.

The left-hand end of the plunger 42 has a shoulder 53 for supporting the base of the metallic cone I6. In some instances it may be desirable to use a special steel cone of same shape as the cone I6 for the molding operation. During the molding operation a cone I6 is inserted into the end of the plunger and a cable with a terminal casing is assembled on the tool as shown in Figs. 2 and 5. The casing 8 of the terminal is then seated againstA the shoulder 39 of the cylinder 34.

As shown in the explo-ded view of Fig. 6, the molding press includes means for clamping in position a cable with a terminal casing thereon. This means includes a cylinder 54 having a threaded portion secured to an anchor plate 55 held on the supporting plate 38 by means of two spaced rods 56. The cable projects centrally through the cylinder and is engaged by means of a three-part clamp 51 bearing against a thrust plate 58 provided with a conical opening 59. The thrust plate is seated against the righthand end of the cylinder 54 and has an opening 60- for accommodating one of the rods 56 and a recess 6i for accommodating the other rod 5B. The rod 56 projects through the opening Bilof the thrust plate and constitutes a pivot for the latter; that is, the thrust plate may be swung into position about the rod 56 so that the other rod 56 slips into the recess 6 I.

During assembly a cable with a terminal casing thereon is inserted through the cylinder 54. Thereupon the three parts of the clamp 51 are positioned about the cable. Then the thrust plate 58 is moved into position to support the clamp and iinally the threaded cylinder 54 is rotated toward the thrust plate 58 in order to force the thrust plate58 up around the clamp which, in turn, engages the terminal casing.

During construction of the joint, it is desirable to strip the cable in a manner such that the amount of compound left on the end portion .is

sufficient to produce the enlarged conical end portion of the dielectric.

lductor` is notsuilicient, additional compound may be placed into the casing in 'the form rof a ringor insulation pellet 62 vas shownin Fig.

'This additional compound is to'be ofthe same vdielectric vmaterial as that on the cable. j ADuring the molding operation, hot air or .like fi heating medium, is admitted through the pipe 36 to the cylinder 34 to heat the insulation until it reaches a certain temperature, for example,

110 C. in case such insulation or dielectric is `made from polyethylene. Thereupon the plunger 42 is slowly 'advanced by rotating the handle 48.

,As the plunger advances, the cone I6 peels back `the dielectric medium on-the cable, and together with the angular end face 43 Aon the plunger,V forces the insulation into the tapered section! .il of the terminal casing.

' Although the molding press and the dielectric compound on the cable 'are heated during Athe 'in'itial stages Vof the molding operation, it is important that lthe dielectric compound be com-'lA pletely cooled upon completion ofthe operation. This is so because `the dielectric, such as polyethylene, contracts upon cooling and it is extremely important thatthere be no voids 'in the dielectric compound after it has been molded i into position. For this reason, during the latter stages of the molding operation, the terminal -and molding press near the cable end of the construction are cooled by means oi a water bath.

vSince .the dielectric compound shrinks oncooling, it is important for the operator to know Whether or not Athe plunger of the molding press of the dielectric compound might laccumulate out of sight in the space between these two members. However, by providing the channel 44, lthe operator can immediately ascertain whether or .not the .plunger is being moved` vat the proper .rate because the excess compound is always `visible.

During the molding operation, the operator fshould move the Vplunger 42 fast enough so that .material is continuously extruded through the vchannel 44 during the entire molding cycle. Moreover, it will be apparent that the rate Aat ,which material is extruded out of the channel '44 will give the operator an indication as to Whether or not the plunger is being moved 'at the `proper speed. If the plunger is moved too -fast during the initial stages of the molding cycle,

then an excess of dielectric `compound will be extruded through the channel `4'4 giving an indication to the .operator to decrease the 'speed l. 'of .the plunger.

' -nnai position at .a time whentne insulation nas jbecomethoroug-hly cooled 1and :shrunk .and fthe plunger vshtnild 'be operated `Vso that the dielectric compound is extruded through the channel 44 `'continuously during movement of the plunger. When this procedure 'is followed, it is practically ycertain that 'there will be no voids in the 'molded vinsulation ofthe terminal.

Upon completion of the molding operation, vthe terminal casing is removed from the press and the gasket 3B is .inserted together with the re- A"taining ring 3|. vThe gasket 30 is held 'in posil'inner surface.

tion by application of pressure on the retaining "ring and then a projection is spun in the cylindrical casing 8 to hold the retaining ring f3| in position. The projection 32 may be formed by rotating the terminal casing on a mandrel. A-lr ternatively, the terminal casing may be held fast and 'a suitable T'forming tool rotated around the periphery of the casing. Finally, the metal cone IB is secured Ato the'inner conductor 'by any suitfable means such as the solder i9. Then the coupling member 24 or 26 is 'fastened to the terminal casing 8.

`In some cases, VVit is not desirable to perform the molding operation of the solid dielectric after la terminal has been :attached 'to the end of a cable section. In suc'h cases I provide a special cable termination or terminal Which has a premolded insert. The insert is made of the same dielectric material 'as that in the cable, or alternatively it may be made of 'a material having 'the same dielectric constant, It `forms a dielectric connection between the ldielectric medium of the cable section andthe air space in the connector `similar to that produced by the ymolding process *at the end of the cable.

Such `a terminal with Aprefabric'ated 'dielectric Icone is illustrated in Fig. '7. It comprises a terfminal casing 63 corresponding vto the casing 8 of the casing and yconnected fto "a threaded sleeve 12 corresponding `to the sleeve 20 of Fig. 1. .A premolded dielectric cone 13wi'th va cylindrical extension 'I4 Lis vdisposed in the casing and has .an outer 'surface engaging the conical surface G8 o'f Vthe casing and an inner surface engaging the metallic cone 110. The cone 'I3 has 'an end face or boundary 15 disposed at a predetermined angle, the angle being determined by the same requirements as the end face 29 in Fig. 1. Generally, a Ypremolded dielectric cone constructed according tothe form .of 'my invention shown by Fig. 7 has inner and 'outersubstantially conical surfaces tapered in the same direction and an end surface which is tapered in the opposite direction and which .extends from the wide end .of the outer surface toward the wide end of the The shape :of the cone is such as to provide va substantially uniform surge impedance.

During lassembly of the `terminal construction `shown by Fig. 7, the braid and :jacket are re- `moved from a J-shor't end portion of the .cable T6. The end face of 'the .solid 'dielectric 'ofthe cable' ris smoothed and the washers 66, 'the Vrings .55,

' the clamp B4-are assembled ion 'the loable.

. a conducting tube or rod of brass, or the like.

The end of the tube is threaded, as indicated at l1. After the insulating cone 'I3 has been placed in position the metallic cone 'l0 is thread- `ed on the end of the conductor and tightened in position. Then the gland nut 6l is tightened while the casing is held in correct position with respect to the cone 'l0 so that the premolded dielectric cone is properly positioned in the terminal casing against the end face of the cable infsulation and against the taperedl surfaces of the terminal casing. The parts should be assembled.

together snugly to prevent the formation of air pockets or voids.

Thus, with my invention I have accomplished an improved cable and cable connector whereby reflection of high frequency waves in the cable is substantially eliminated and whereby the characteristic or surge impedance remains substantially constant throughout the cable lengths and joint. The method of attaching the connectors to the cable is one which may be performed equally as well in the eld as in the factory. Connectors constructed in accordance with my invention are simple in construction and are especially suitable for making joints in field use.

Having described the method of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. An electric cable comprising two sections and a connector between them, said sections having respectively inner and outer conductors with at least one section having a solid dielectric therebetween, said connector having an outer casing including non-linear convex tapered portions for electrically connecting the outer conductors of the sections and connecting means centrally disposed Within and spaced from said casing including non-linear concave tapered portions for electrically connecting the inner conductors of the sections, the space between said tapered portions adjacent said cable section having a solid dielectric being illled with a solid dielectric and the balance of the space between said casing and said centrally disposed connecting means being lled with a dielectric other than that of said cable section, said solid dlelectric between said tapered portions terminating in a boundary surface located at an angle to the direction of electric wave propagation such that the characteristic surge impedance of the connector is substantially the same on each side of the boundary and such that reflection of waves at the boundary is substantially precluded, said boundary angle being such that where B is the angle of incidence of an electric wave, K1 is the dielectric constant on the side cot B= of incidence and K2 the dielectric constant on medium, means including anon-linear' concave tapered portion as part of said inner conductor and a non-linear convex tapered portion as part of said outer conductor connecting the conductors of the terminal to those of the casing and a portion of the solid dielectric material of the cable extending into the terminal between said inner and outer conductors, said tapered portions diverging away from each other in a direction toward the portion of said terminal having said gaseous dielectric medium as the insulation between said inner and outer conductors and said solid dielectric terminating in aboundary located at an angle to the direction of electric wave propagation such that the characteristic' surge .impedance of the terminal is substantially the same on each side of the boundary and such that renection of waves at the boundary is substantially precluded, said boundary angle being such that where B is the angle of incidence of an electric wave, K1 is the dielectric constant on the side of incidence and K2 the dielectric constant on the side of refraction.

3. A terminal for use with a cable comprising, in combination, a conducting casing having a spaced inner conductor, a gaseous dielectric material in a portion of said casing insulating said casing irom said conductor and a solid dielectric material in said casing likewise insulating said casing and said conductor, said casing having a non-linear convex tapered portion and said inner conductor having a non-linear concave tapered portion respectively diverging away from each other in the direction towards the portion of said casing and said inner conductor insulated by said gaseous dielectric material, said solid dielectric material forming with the gaseous dielectric a boundary located at an angle in the direction of electric wave propagation such that the characteristic surge impedance of the terminal is substantially the same on each side of the boundary and such that reflection of waves at the boundary is substantially precluded. said boundary angle being such that where B is the angle of incidence of an electric wave, K1 is the dielectric constant on the side of incidence and K2 the dielectric constant oi.' the side of refraction.

4. A terminal for use with a cable having concentric conductors adapted to transmit a high frequency wave comprising, in combination, a conducting casing having a spaced inner conductor insulated from said casing by a dielectric gas, said inner conductor having a non-linear concave tapered portion and said casing having a non-linear convex tapered portion for connecting said casing and said inner conductor with the concentric cable conductors and a solid dielectric material insulating said tapered portions, said tapered portions diverging away from each other in a direction toward the portion oi' said casing and said inner conductor insulated by said dielectric gas and said solid dielectric material having an interface with the gas dielectric forming a boundary surface located at an angle to the direction of electric wave propagation such that the characteristic surge impedance oi the terminal is substantially the same on each side of the boundary and such :that faction gai waves at `the boundary isi subsrstalntially-gpneeluded, auch Jboundaryfangle bei-ng meh .tht Y y l jwhene, is the. wangle of vinc-:lic'ermetui `an electric wave K1l iris the dielectric czcmstant on .the side ,of

incideceend K2 thedelectric Yconstant of the sdeefzfrefmcton.

. WETHERILL.

REFERENCES CITED The 'z'folfowing references are `of 'recerd in the me DI' :this @pantera-,t2 y

.Number Name 'Date Gulentz 'May 19, 1903 Miller et al. Apr. 26, -1904 Green Jan. '19, '1932 Clavier Oct. 31, 1933 Southworth Sept. 13,1938 Cork Yet a1. July 9, 1940 Bishop J une '23, 1942 kFel-1 Sept. 3, 11946 FOREIGN PATENTS Country A Date Switzerland Sept.. 16,1943 

